Fixation and stabilisation of fractures can be difficult, especially in long bones. Two techniques are normally used. The first technique involves placing a plate on one side of the bone and screwing the plate to the bone on either side of the fracture with a plurality of screws. This technique suffers from the disadvantage that forces are applied to the bone via the screws from one side of the bone only, which can cause uneven loading on the bone.
The second technique for fixation and stabilisation of fractures involves inserting an intramedullary pin into the medullary canal of the bone. Fixation pins may or may not be used. If fixation pins are not used, the bone at either side of the fracture may rotate around the intramedullary pin which leads to misalignment of the bone. If fixation pins are used, it is necessary to drill holes through the bone on either side of the fracture and insert fixation pins through the holes in the bone with those in the intramedullary pin, thereby complicating the operative procedure and potentially causing an increase in post-operative recovery time for the patient.
Fixation of prosthesis, such as artificial hips and artificial knees, also faces similar difficulties. For example, fitting an artificial hip to a patient typically involves preparing the upper part of the femur and inserting a stem portion of the hip prosthesis into the medullary canal of the femur. The stem is fixed to the femur by bone cement or by inserting external pins through holes drilled through the femur and into and through holes in the stem portion of the artificial hip. The difficulties with using external pins have been discussed above. In cases where bone cement is used, misalignment and shifting of the prostheses can occur if the cement does not adequately adhere to the bone.
My Australian patent no. 755111 describes an intramedullary bone fixation device which uses a plurality of extendable pins to fix the device to the bone. In use of this device, the device is inserted into the medullary canal of a bone and the pins extended such that they extend into the bone surrounding the medullary canal to thereby fix the device to the bone. The entire contents of my Australian patent no. 755111 are herein incorporated by cross-reference.
FIG. 13 of my Australian patent no. 755111 shows an intramedullary bone fixation device that is of expandable length. This device includes an inner member having first and second portions and an outer member having first and second portions. The first portion of the inner member includes a bore having a threaded portion. A bore is also included in the second portion of the inner member, with the bore of the second portion terminating in a blind end. A screw is threadably inserted into the bores of the inner member pieces. When the screw has been fully inserted, the end of the screw strikes the blind end. Further rotation of the screw then acts to expand the length of the inner member by pushing apart the two portions of the inner member. As the pins have been inserted into the bones surrounding the medullary canal, extending the length of the inner member also extends the length of the outer member. The device shown in FIG. 13 of my earlier Australian patent number 755111 is used by pre-setting the device at a desired length. However, once the length of the device has been set, it is a static device. The screw locks the proximal and distal components in the desired pre-set position.
The device shown in FIG. 13 of my earlier Australian patent no. 755111 can suffer from the following problems:
a) the screw can become stuck when it contacts the end of the blind bore in the second part of the inner member. This problem is exacerbated by the threaded screw being in threaded engagement with the bore in the second member and the combination of the threaded engagement and contact with the blind end of the bore making it very difficult, if not impossible, to further turn the screw; and
b) the device shown in FIG. 13 of my earlier Australian patent no. 755111 is not able to shorten the length of the device because turning the screw in the opposite direction simply unscrews the screw from the threaded bores.
My earlier international patent application no. PCT/AU0301207, published as WO 2004/026158, relates to fixation devices which include pins that can be moved from a retracted to an extended position. The entire contents of my earlier international patent application no. PCT/AU03/01207 are also incorporated herein by cross-reference.
The applicant does not concede that the prior art discussed herein forms part of the common general knowledge in this art in Australia.
Throughout this specification, the terms “comprising” and its grammatical equivalents are to be taken to have an inclusive meaning unless the context indicates otherwise.
The applicant does not concede that the prior art discussed in this specification forms part of the common general knowledge in Australia or any other country.